1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to devices and methods for performing minimally invasive direct cardiac massage.
Sudden cardiac arrest is a leading cause of death in most industrial societies. While in many cases it is theoretically possible to re-establish cardiac function, irreversible damage to vital organs, particularly the brain and the heart itself, will usually occur prior to restoration of normal cardiac activity.
A number of techniques have been developed to provide artificial circulation of blood to oxygenate the heart and brain during the period between cardiac arrest and restoration of normal cardiac activity. Prior to the 1960""s, open chest cardiac massage (OCM) was a standard treatment for sudden cardiac arrest. Open chest cardiac massage, as its name implies, involved opening a patient""s chest and manually squeezing the heart to pump blood to the body. In the 1960""s, closed chest cardiac massage (CCM) where the heart is externally compressed through the chest wall became the standard of treatment. When CCM is combined with airway support, it is known as cardiopulmonary resuscitation (CPR). CPR has the advantage that it is much less invasive than OCM and can be performed by less skilled individuals. It has the disadvantage, however, that it is not generally effective. In particular, the medical literature shows that CCM provides significantly less cardiac output, neuroperfusion, and cardiac perfusion than achieved with OCM.
Methods and devices for performing minimally invasive direct cardiac massage have been described by Buckman et al. and by Drs. Filiberto and Giorgio Zadini in the patent and literature publications listed in the Description of the Background Art below. While the methods of Buckman et al. and the Zadinis differ in a number of respects, they generally rely on introducing a balloon, shoe, or other deployable member to engage the heart through a small incision through an intercostal space above the pericardium. The heart may then be pumped by directly engaging and compressing the pericardium, either by inflating and deflating the member or by reciprocating a shaft attached to the member. Although these approaches have been shown to be effective in animal models, the particular devices described in the patents are awkward for emergency use on human patients. In particular, the balloon-type and shoe-type heart-engaging members described in the patents may be difficult to deploy in the potential space between the posterior surface of the rib cage and the pericardium. For example, inflatable balloon members may lack sufficient rigidity to impart the necessary compressive force, rigid shoe-like members risk damage to the pericardium, and cup-shaped compressive members may compress so much of the heart volume that the end diastolic volume is compromised.
For these reasons, it would be desirable to provide improved methods and devices for performing minimally invasive direct cardiac massage. In particular, it would be desirable to provide apparatus and methods which are simple to deploy and carry out and in particular which do not require intervention by a physician. The heart-engaging component(s) of the devices should reliably deploy and expand within the region between the posterior rib cage and the pericardium and should minimize risk to the pericardium from perforation and other damage. The devices and methods should be simple to introduce to the patient in the first place, and in at least some circumstances, should eliminate the need to separately make an incision before introducing the device. The apparatus and method further should be compatible both with manual actuation, i.e., manual reciprocation of a handle or shaft attached to the heart-engaging member, and with automatic or powered systems for reciprocating the member. At least some of these objectives will be met by the invention described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 5,582,580; 5,571,074 and 5,484,391 to Buckman, Jr. et al. and 5,683,364 and 5,466,221 to Zadini et al., licensed to the assignee of the present application, describe devices and methods for minimally invasive direct cardiac massage through an intercostal space. Published PCT application WO 98/05289 and U.S. Pat. No. 5,385,528 describe an inflatable device for performing direct cardiac massage. U.S. Pat. No. 3,496,932 describes a sharpened stylet for introducing a cardiac massage device to a space between the sternum and the heart. Cardiac assist devices employing inflatable cuffs and other mechanisms are described in U.S. Pat. Nos. 5,256,132; 5,169,381; 4,731,076; 4,690,134; 4,536,893; 4,192,293; 4,048,990; 3,613,672; 3,455,298; and 2,826,193. Dissectors employing inflatable components are described in U.S. Pat. Nos. 5,730,756; 5,730,748; 5,716,325; 5,707,390; 5,702,417; 5,702,416; 5,694,951; 5,690,668; 5,685,826; 5,667,520; 5,667,479; 5,653,726; 5,624,381; 5,618,287; 5,607,443; 5,601,590; 5,601,589; 5,601,581; 5,593,418; 5,573,517; 5,540,711; 5,514,153; and 5,496,345. Use of a direct cardiac massage device of the type shown in the Buckman, Jr. et al. patents is described in Buckman et al. (1997) Resuscitation 34:247-253 and (1995) Resuscitation 29:237-248.
The present invention provides improved devices and methods for performing cardiac massage, particularly minimally invasive direct cardiac massage where the heart is directly compressed through a small incision formed through an intercostal space over the pericardium. Devices according to the present invention comprise a support and a heart-engaging member attached to the support. The support may be any assembly, structure, system, or other mechanical framework which is suitable for positioning and manipulating the heart-engaging member so that it can engage and compress the heart. Most simply, the support could be a simple handle or shaft having the heart-engaging member attached at a distal end thereof. Once the heart-engaging member is deployed, cardiac massage can be performed by simple manual pumping or reciprocation of the handle or shaft. In the exemplary embodiment described hereinafter, the support comprises a shaft together with a sheath which is coaxially received over the shaft. The shaft and sheath may be manipulated relative to each other to deploy and retract the heart-engaging member, as described in more detail hereinbelow. A wide variety of other supports will also be possible, including supports which comprise powered drivers, such as electric, pneumatic, or other motors. Such drivers can be provided as part of the support, where the driver may be disposed externally, internally, or both externally and internally relative to the patient when the heart-engaging member is deployed over the pericardium.
The heart-engaging member of the present invention comprises a plurality of struts which are reciprocatably attached to the support. The struts are retractable to a radially contracted configuration and advancable along arcuate, diverging paths to define a surface which non-traumatically engages the pericardium to compress the heart when advanced against the pericardium: The struts will typically be composed of a resilient material, more typically be composed of a shape memory alloy, such as nickel titanium alloy, and will usually be formed to deploy radially outwardly and advance along the desired arcuate, diverging paths as they are advanced from a constraining member, usually a tubular sheath. The struts may be advanced and retracted relative to the sheath using any suitable mechanical system, typically a shaft which reciprocates together with the struts through a lumen of the sheath. In some instances, it will be desirable to provide at least some of the struts with a temperature-responsive memory so that the shape of the struts will change in response to a transition from room temperature to body temperature and/or in response to an induced temperature change after they have been deployed, e.g., by electrically heating or cooling the struts and/or infusing a heated or cooled medium into the space surrounding the struts.
The geometry of the retracted strut configuration will be selected to facilitate introduction through the intercostal space before strut deployment. Preferably, the struts will be contracted within a space having a maximum width of 2 cm, preferably a maximum width of 1.2 cm. After deployment by advancing the struts along the arcuate, diverging paths, the heart-engaging surface which is defined will have a surface area of at least 5 cm2, preferably being in the range from about 10 cm2 to 100 cm2, usually in the range from 20 cm2 to 75 cm2. Usually, the surface will be generally circular or slightly oval with a diameter or average diameter in the range from 3 cm to 18 cm, preferably from 5 cm to 10 cm.
An important advantage of the present invention is that the struts may be radially deployed with only a minimum axial advancement. That is, the struts will make a sharp radially outward turn from the support as they are advanced into the region between the pericardium and the posterior rib cage. Typically, the distal tips of the struts will advance no more than 5 cm in the axial direction before they are fully radially deployed. More preferably, the maximum axial distance will be 2 cm or less, even more preferably being 1.5 cm or less, and still more preferably being 1 cm or less.
In another preferred aspect of the present invention, the surface defined by the plurality of struts will comprise a flexible sheet attached to at least some of the struts. The sheet will usually, although not necessarily, be inelastic or non-distensible, permitting it to readily conform to the surface of the pericardium as the struts are advanced while constraining the deployed tips of the struts and preventing the struts from bending back from the heart. Alternatively or additionally, the tips of the struts may be constrained by a filament, strip, suture, or other element which ties the tips together and prevents over deployment and expansion of the struts. The sheet may be continuous, i.e., in the form of a continuous fabric, membrane, or the like, or may be discontinuous, i.e., in the form of a net, perforate sheet, permeable or impermeable sheet, or the like. Optionally, the strut may be flat (when not engaged against the pericardium) or may be slightly concave to conform to the exterior surface of the pericardium.
Alternatively or additionally, an inflatable bladder may be attached to at least some of the struts. The inflatable bladder may comprise a generally flat structure extending over all the struts, or may comprise an annular or torroidal structure extending over only the outer regions of the struts. The bladder may be inflatable using a liquid or gas, preferably be inflatable with a physiologically acceptable liquid, such as saline, contrast medium, or the like.
In a still further preferred aspect of the apparatus of the present invention, the support may include a blunt member which can bluntly dissect a space between the anterior surface of the intercostal muscle and the posterior surface of the rib cage in order to facilitate deployment of the struts into the space. For example, the blunt member may be provided as a leading edge or tip of the support which enters through the intercostal space into the region over the pericardium. The struts may then be advanced through or over the blunt member, or the blunt member may be retracted prior to strut deployment.
In a particularly preferred embodiment of the device of the present invention, a blunt member will be provided as the leading edge of the support. The blunt member may include a blade which may be axially advanced from the blunt member, point, or other cutting element to make an incision partially through the skin overlying the intercostal space before the blunt member is introduced through the intercostal space. Usually, the blade or other cutting element will be automatically retractable so that the blade cannot enter into the space immediately above the pericardium in order to reduce the risk of injury to the pericardium and the heart. By providing the blade and blunt member on the cardiac massage apparatus, the device can be introduced in a single step with minimum preparation of the patient prior to such introduction. The user need only properly locate the cardiac massage device over the intercostal space and then advance the device through the skin prior to radially deploying the struts to engage the pericardium.
Methods according to the present invention for performing cardiac massage comprise advancing a plurality of struts through an intercostal space to a region over a pericardium. The struts are opened along arcuate, radially diverging paths (to form a trumpet horn geometry) between a posterior rib surface and the pericardium. The open struts are then engaged against the pericardium to periodically compress the heart and induce artificial blood circulation. Preferably, the struts are introduced by first bluntly dissecting a space between the posterior rib surface and the pericardium, typically by advancing a blunt member through the intercostal space, where the blunt member is disposed between the struts. Optionally, a blade may be advanced from the blunt member to partially cut through the intercostal skin, where the blade is retracted prior to advancing the blunt member into the space between the ribs and the pericardium. Still further optionally, a flexible sheath may be unfurled as the struts are open. Alternatively, an inflatable bladder may be attached to at least some of the struts and be inflated as the struts are deployed and/or to effect deployment of the struts.
In another aspect of the method of the present invention, cardiac massage is performed by engaging a plurality of struts arranged in radially diverging arcuate paths against the pericardium. The struts are then reciprocated against the pericardium to induce artificial circulation. Usually, either a flexible sheet or an inflatable bladder will be suspended between at least some of the struts as the struts are reciprocated.
In a still further aspect of the methods of the present invention, the region between a posterior rib surface and a pericardium may be bluntly dissected by advancing a blunt member through an intercostal space into said region. In particular, the advancement is enhanced by deploying a blade from the blunt member to partially cut through the intercostal skin prior to advancing the blunt member. Preferably, the blade is automatically retracted back into the blunt member before the blunt member can pass completely through the skin and the intercostal space.